Estimations of the direction of view of a human observer are used in a wide variety of technical systems. For example, Trefflich, in the treatise “Videogestütze Überwachung der Fahreraufmerksamkeit und Adaption von Fahrerassistenzsystemen” (“Video-supported monitoring of driver attentiveness and adaptation of driver assistance systems”), (Technische Universität Ilmenau, 2010), describes a method for estimating the direction of view of the driver of a vehicle as a function of his current head orientation. This estimation is then used to ascertain whether the driver still has the roadway in view and is attentively following the traffic situation, in order if necessary to adapt the behavior of driver assistance systems, e.g., warning systems.
A more precise estimation of the direction of view of an observer can be obtained from measurements of the eye movements of the observer. Eye movements can be measured using video-based head and/or eye tracking systems, i.e., tracking systems for head and/or eye movements of the observer. These systems standardly first estimate the head movements of the observer on the basis of clear facial features. In a second step, the eye and specific eye features—e.g., the pupils, the sclera, or the corneal reflection—of the observer are acquired. These features are used to estimate the eye rotation and to supply a more precise estimation of the direction of view of the observer.
For example, PCT Published Application WO 01/052722 A1 describes a device for acquiring the direction of view of a user having a light source that is configured to produce a light beam in the direction of the eyes of the user, and having a detector for acquiring the light beam when it is reflected in the eye.